Cancer screening
癌症筛查
Seeing is not always relieving
眼不见心不烦 （陈继龙 译）
Mar 8th 2007
From The Economist print edition
Screening for lung cancer may do more harm than good
肺癌筛查可能弊大于利
SOMETIMES you can know too much. The aim of screening healthy people for cancer is to discover tumours when they are small and treatable. It sounds laudable and often it is. But it sometimes leads to unnecessary treatment. The body has a battery of mechanisms for stopping small tumours from becoming large ones. Treating those that would have been suppressed anyway does no good and can often be harmful.
有时候你可能知道得太多了。健康人群癌症筛查的目的是发现可治疗的小肿瘤，这似乎是值得称赞的，而事实常常也是如此。不过，有时它会导致不必要的治疗。机体自身有一套阻止小肿瘤生长的机制，对那些可用自身机制加以抑制的肿瘤采取治疗非但无益，反而可能造成危害。
Take lung cancer. A report in this week's Journal of the American Medical Association, by Peter Bach of the Memorial Sloan-Kettering Cancer Centre in New York and his colleagues, suggests that, （1）despite much fanfare around the use of computed tomography (CT) to detect tumours in the lungs well before they cause symptoms, the test may not reduce the risk of dying from the disease at all—indeed, it may make things worse.
以肺癌为例。纽约纪念斯隆-凯特灵癌症研究中心（Memorial Sloan-Kettering Cancer Centre）的彼得•巴赫（Peter Bach）及其同事在本周出版的《美国医学会杂志》（Journal of the American Medical Association）上发表的一项报告中指出，用于症状出现前肺部肿瘤检测的计算机断层扫描技术（computed tomography，CT）虽深受吹捧，但它可能根本无法降低肺癌死亡率，相反会“雪上加霜”。
The story begins last year, when Claudia Henschke of Cornell University and her colleagues made headlines with a report that patients whose lung cancer had been diagnosed early by CT screening had excellent long-term survival prospects. Her research suggested that 88% of patients could expect to be alive ten years after their diagnosis. Dr Bach found similar results in a separate study. In his case, 94% of patients diagnosed with early-stage lung cancer were alive four years later.
有关CT用于肺癌筛查的报道始于去年。康奈尔大学克劳迪娅•赫恩施克（Claudia Henschke）和她的同事报道，患者经CT早期诊断为肺癌后，长期生存率显著提高。这一报道轰动一时。她的研究发现，88%的确诊患者10年后仍有望存活。巴赫在另一研究中也发现了类似结果：94%诊断为早期肺癌的患者生存期可达4年。
Survival data alone, though, fail to answer a basic question: “compared with what?” People are bound to live longer after their diagnosis if that diagnosis is made earlier. Early diagnosis is of little value unless it results in a better prognosis.
尽管如此，仅凭生存期的统计数据是无法回答这样一个基本问题的：“与什么相比？”早期诊断无疑可延长生存期，但早期诊断后患者预后必须良好，否则早期诊断就几乎无任何价值。
Dr Bach, therefore, interrogated his data more thoroughly.（2） He used statistical models based on results from studies of lung cancer that did not involve CT screening, to try to predict what would have happened to the individuals in his own study if they had not been part of that study. The results were not encouraging.
因此，巴赫对自己的数据进行了更为彻底的分析。他根据非CT检出肺癌的研究结果建立了统计学模型，并假设其研究个体未接受CT筛查，从而对这些个体的预后进行了评估，结果令人失望。
Screening did, indeed, detect more tumours. Over the course of five years, 144 cases of lung cancer were picked up in a population of 3,200, compared with a predicted number of 44. Despite these early diagnoses, though, there was no reduction in the number of people who went on to develop advanced cancer, nor a significant drop in the number who died of the disease (38, compared with a prediction of 39). （3）Considering that early diagnosis prompted a tenfold increase in surgery aimed at removing the cancer (the predicted number of surgical interventions was 11; the actual number was 109), and that such surgery is unsafe—5% of patients die and another 20-40% suffer serious complications—the whole process seems to make things worse.
筛查确实可以发现更多的肿瘤病例。五年中，3200人有144人检出肺癌，而预期值仅为44例。不过，尽管这些人得到早期诊断，但发展为晚期肺癌的人数并未减少，死亡人数也无显著下降（预期为39人，实际有38人）。考虑到早期诊断可使行肿瘤切除术的人数增加十倍（预期为11人，实际达109人），而这种手术风险又大（术后死亡率5%，此外还有20~40%的患者出现严重并发症），如此一来就有可能造成更大危害。
（4）Dr Bach's conclusion is that many of the extra cancers picked up by CT screening would never have caused clinical disease, while the most agGREssive tumours—those that cause most of the 160,000 lung-cancer deaths in America each year—grow too quickly to be found early, even with annual CT screening. The situation resembles prostate-cancer screening, which relies on a blood test for a molecule secreted by prostate tumours. In prostate screening, a lot of disease is identified, but there is great doubt over the number of lives this saves. Dr Bach's research also resembles an earlier attempt to deal with lung cancer, in which researchers uncovered 20% more tumours in groups that underwent screening using chest X-rays than in those who did not. Then, too, the frequency of death from the disease did not differ between the two groups. Both Dr Bach and Dr Henschke had hoped that by using CT, which is better than X-rays at picking up small tumours in the lungs, they might have changed this outcome.
巴赫认定，许多经CT筛查新发现的肿瘤根本不会引发临床表现，而侵袭性极强的肿瘤——美国每年死于肺癌的16万人中多数都由此引起——由于生长过快，即便每年用CT筛查也无法及早检出。这一情形与前列腺癌筛查类似。后者对血液中前列腺肿瘤分泌的一种分子进行检测以达到筛查目的。筛查检出了许多前列腺癌患者，但因此得以生存的人数却尚难知晓。与巴赫研究类似的还有早前一项肺癌治疗的研究。当时研究人员发现，接受胸部X光透视的人群中所发现的肿瘤患者人数要比未接受透视的人群高出20%，但两组死亡率同样无差异。巴赫和赫恩施克都希望应用CT这一在肺部小肿瘤检测方面优于X光片的技术，来改变这一结果。
Dr Bach was comparing data from screened people with a model of what would have happened to an unscreened group.（5） The final word on CT screening for lung cancer will have to wait for the results of a proper experiment that compares screened and unscreened groups. These are expected in the next year or two. The omens, however, are bad. What you do know can hurt you.
巴赫对接受筛查人群的有关数据与未接受筛查人群的预后模型进行了比较。CT筛查肺癌到底是好是坏，只有等到这两组人群对比试验的结果出来以后才会见分晓，预计是在明后年。然而，目前看兆头可不好。懂得越多，伤得越深。
